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MGB GTV8

Published: 11th Jul 2011 - 0 Comments - Be the first, contribute now!
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MGB GTV8
MGB GTV8
MGB GTV8
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Which classics still have the potential to get up and go? Alan Anderson remembers the cars, the tuners and the tweaks and tells why they’re still hot!

Too little, too late – that was the reaction from the motoring press when the MGB GT V8 was fi nally launched in 1973, just before the fuel crisis! Slotting in the evergreen Rover V8 unit seemed so logical you wonder what took BL so long, especially since Mini racer extraordinaire Ken Costello did it at the turn of the previous decade, coinciding when British Leyland was dropping the unloved and poorly-developed MGC. Unquestionably that compact and lightweight V8 that powered Rovers was just made for the MGB and even though BL refused to offer it in Roadster form (fearing the shell wasn’t up to it, even though Costello proved it was!), the GT made an excellent sports hatch, if a little old fashioned one for a 1973 car. It also started a wave of DIY conversions and even Austin Rover, as it was then known, decided to have a more adventurous go at it when it brought the old MGB back to life in the early 1990s with the re-engineered, fuel injected MGR V8. There’s no doubt about it, a V8 MGB of any description makes a good road car – here’s how to make one ever better!

Get One Now

With this old V8 you can tune it or simply increase the capacity

The great thing about the MGB V8 – whether it’s factory made or home-spun, is that it cost little more than a standard 1.8 to buy and keep. This includes the MGR model, which has more than ample go in standard tune. The only exception is the Costello conversion, which now seems to attract a signifi cant premium. Mechanically the V8 is almost burst-proof, so long as the oil has been changed regularly to avoid sludging, which will hinder and hurt the hydraulic tappets. The only other issue is in the retention of the cylinder heads, which may effect MGBs that have been converted to V8 power. Buick engines had 18 retaining bolts for each head, whereas on SD1 motors one outer row of four bolts is not used and this creates uneven stress on one side. This does not necessarily cause the head gasket to blow, but allows unspent petrol and exhaust fumes to ‘weep’ into the centre of the Vee and contaminate engine oil, resulting in bore wear and cam and crank bearing failures. Rover did not fi nally solve the problem until 1994, when the other row of four bolts was deleted and the heads were attached to the block by just 10 equally spaced bolts. A ‘fi x’ for 14-bolt heads is to torque down the centre two rows of fi ve and simply leave the outer four fi tted but un-tensioned and ‘Loctited’ in place. The V8 uses a lot of stock MGB running gear, albeit beefed-up, and so is well proven. By far the biggest worry with any old MG is body rot which can be bad; the sill structure and inner wings are particularly critical. If the worst comes to the worst, then you can always by a brand new bodyshell from British Motor Heritage.

Hotting One Up

The engine that Rover inherited from Buick was already old when it arrived on UK shores. Earliest versions had rope oil seals on the crankshaft and main bearing caps that were apt to ‘fl oat’ and knock out the bearings. Rover’s development of the engine was somewhat reluctant, but by 1982 most of the major problems had been ironed out – including neoprene oil seals and a stiffer alloy block with cross-bolted mains caps. ‘Stiff’ blocks can be identifi ed by wider and more uniform strengthening webs in the centre of the Vee between the cylinder banks, and the crossbolted type by the bolt heads low down along the sides of the block. The V8 has enjoyed a long and legendary service life. Of course, the factory MGB GT V8 used the unit in lower compression Range Rover tune and this dropped the power down by almost 20bhp. Simply fi tting, or converting the engine to Rover saloon tune, may prove ample for many owners, as the difference is certainly noticeable and of course means that the engine doesn’t further tweaking. Post SD1, Rover upped the power by increasing capacity. The original 3528cc engine has 89.5mm bore and 71mm crank throw, with the later 3.9-litre unit achieved by using 94mm bore. When the engine went to 4.2-litre, the crank was changed to one with a 77mm throw and the 4.6 litre unit is obtained by further stroking to 82mm. The 94mm bore is as large as can be
safely obtained within the block, and some of these engines have been known to crack behind the cylinder liners. While upping capacity is a sure way to increase power, there’s plenty of scope for modifi - cation of the heads. Careful attention to the shape the ports, and matching to the appropriate manifolds, is worthwhile, as is cleaning out the shallow dish-shaped combustion chambers. Valve guide bosses can also be shortened and smoothed to improve gas fl ow, and valve throats opened out. Standard 39.9mm inlet and 34.3mm exhaust valves are fi ne for road tune engines, while 41.4mm inlet and 35.5mm exhaust are about as far as you can usefully go.

A 9.75:1 compression ratio is best for most purposes; with so little chamber in the cylinder head, this is usually obtained by the correct combination of pistons and the type of gasket used, either tin or much thicker composite type. With valve seat inserts used in the alloy heads, damage due to the use of unleaded fuel is not a problem. A camshaft change should be a priority, as this engine benefi ts from better breathing. If you stay with the hydraulic tappets (and there’s not much point in swapping to solid lifters on a road engine) the engine is limited to just over 6000rpm and so tuning for good mid-range torque rather than revs is the best way to go. The timing gear and chain on early engines is likely to wear and warrants fi tting a Duplex set-up, although this is not practical on post 1994 engines. Hand in hand with any cam change must come an overhaul of the ignition system. Most original distributors are likely to be well worn by now and so the only way to go on an early (pre GEMS management system) engine is to fi t a Mallory distributor. This operates as a sixvolt system (retaining 12 volt for starting) and so needs its own coil and ballast resistor. Early SD1 engines were fi tted with either SU or Zenith- Stromberg carburettors, and with these new needles and some fi ne tuning can accommodate mild stages of tune on a rolling road, but the fi rst fuel injection systems (Lucas L-Jetronic) are fairly crude on the electronic front and are not responsive to performance chipping. Really the best course of action for anyone with a pre-GEMS engine looking for a decent increase in power is to fi t a four-barrel Weber carburettor conversion, which sits in the centre of the Vee mating the carb to an Offenhauser inlet manifold. Other carburettor installations have been tried – notably BL fi tted both Pierburg fuel injection and four Weber DCOE carbs on the rally TR8’s. And of couse being a Yank engine, a good old Holley ‘jug’! But for a decent power hike, increased response, and simplicity of installation at fairly reasonable cost, the four barrel Weber is now the best bet if not exactly the cheapest route. As an indication, a pair of modifi ed heads, fast road camshaft, four barrel Weber carb and some decent extractor exhaust ‘headers’ will see the basic 3.5-litre nudge the 200bhp mark; up it 3.9-litres and 250bhp is available – which is plenty for road as well as mild competition use. Incidentally, the Rover lump is still the best choice reckon experts as many other American V8s are too heavy and still can’t match the horsepower.

Handling The Power

For a good many owners, a standard MGB V8 (GT or Roadster) is more than brisk enough, especially if it’s been set up on a rolling road to fi ne tune the ignition and fuelling for a few extra horses. No, the real speed can come from making the most of what it already has, by tuning the chassis. In standard guise, the V8 GT uses pretty well stock MGB running gear, save for a raised ride height (like 1974 MGBs) and stiffer (‘Police’) rear springs. The old lever arm dampers are normally adequate if uprated (but do go for good quality manufacturers) although a front and rear conversion to telescopics is available – the rear being the simplest to do but the ride is affected. The ultimate conversion at the front is to fi t the complete front axle from the MGR V8 and then you’ll also benefi t from much better brakes at the same time. Poly bushing is an extremely worthwhile mod but the ride and refi nement will further suffer. The MGR V8 has most of the kit you need for better handling – apart from the cheapskate dampers fi tted by the works when new. Uprated Koni or Spax units are said to transform the car – speak to a specialist like Clive Wheatley who really knows these cars. MGB GT V8 brakes were just mildly beefed-up MG 1.8 ones and a variety of options is now available. A thorough overhaul using EBC Greenstuff pads is worthwhile, even for standard tune cars. Don’t go mad on fat tyre sizes either; slightly larger than stock size is about the best for road use but use good quality rubber.

How Did It Drive?

In many ways the MGB GT V8 is better received now than when it was new. Back in 1973, the car was criticised, not for its lack of performance but for being old fashioned elsewhere – like the handling and ride, excessive wind noise and a dated cockpit environment. However, now that this MG is a classic, all this is part of the car’s charm. The MGR V8 feels a bit like a modern take on the old Big Healey and, of course, it comes with fi ve speeds instead of overdrive. The chassis is usefully improved over the original MGB but still keeps that classic feel. On all models, the V8 is beautifully docile and so, when you’re not in the mood for haring around, it becomes a lazy two-gear car, meaning you can have the best of both words with this MG. The MGR is better sorted as you’d expect, and goes very smartly indeed while the MGR’s chassis revisions by and large work, especially if power steering is fi tted.

Handling The Power...

For a good many owners, a standard MGB V8 (GT or Roadster) is more than brisk enough, especially if it’s been set up on a rolling road to fi ne tune the ignition and fuelling for a few extra horses. No, the real speed can come from making the most of what it already has, by tuning the chassis. In standard guise, the V8 GT uses pretty well stock MGB running gear, save for a raised ride height (like 1974 MGBs) and stiffer (‘Police’) rear springs. The old lever arm dampers are normally adequate if uprated (but do go for good quality manufacturers) although a front and rear conversion to telescopics is available – the rear being the simplest to do but the ride is affected. The ultimate conversion at the front is to fi t the complete front axle from the MGR V8 and then you’ll also benefi t from much better brakes at the same time. Poly bushing is an extremely worthwhile mod but the ride and refi nement will further suffer. The MGR V8 has most of the kit you need for better handling – apart from the cheapskate dampers fi tted by the works when new. Uprated Koni or Spax units are said to transform the car – speak to a specialist like Clive Wheatley who really knows these cars. MGB GT V8 brakes were just mildly beefed-up MG 1.8 ones and a variety of options is now available. A thorough overhaul using EBC Greenstuff pads is worthwhile, even for standard tune cars. Don’t go mad on fat tyre sizes either; slightly larger than stock size is about the best for road use but use good quality rubber.


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